1. Field of the Invention
The present invention relates to a process of producing a parallel type of stripe filter which is used for a color television camera and the like when a color television signal is to be obtained by using an image pickup tube.
2. Description of the Prior Art
A target plate is incorporated into an image pickup tube used for a handy color camera and the like which obtains a color signal by using a single image pickup tube. Such target plate is that prepared by processing a filter material into a striped configuration in order to extract three color signals.
In the target plate incorporated into an image pickup tube used in the phase separation system, two-three kinds of stripe filters are aligned at the edge and arranged in parallel for the purpose of extracting two or three color signals. The accuracy in the alignment of these stripe filters directly affects the obtained image, and therefore, it is required to increase the accuracy in the alignment. It is a serious problem in the art how such accuracy in the alignment at the edge of the stripe filters is increased.
A process hitherto used for producing a stripe filter for extracting three color signals comprises preparing separately three kinds of stripe filters for extracting different three color signals in such a manner that a filter material is vapor-deposited onto a glass base plate and then it is mechanically cut into a striped configuration, and aligning the separately prepared three stripe filters at the edge and further super-imposing them on one another.
In alternative process so far employed for producing a stripe filter for extracting three color signals, three kinds of stripe filters are separately prepared in such a manner that a groove is formed on a glass base plate in a striped configuration and the striped groove is filled up with a filter material, and then the three stripe filters thus separately made are aligned at the edge and superimposed on one another.
Further, another process of producing a stripe filter is proposed and disclosed in Japanese Laid Open No. 37236/1972. Each step of this process is similar to that shown in FIGS. 1A through 1F which will be again referred to later. Such process will be explained with reference to those figures.
As shown in FIG. 1A, onto a glass base plate 1 is vapor-deposited a metal capable of being easily etched, for example copper, to form a metal layer 2, and then a photoresist 4 is coated uniformly on the metal layer 2 as illustrated in FIG. 1B. A stripe photomask 3 having a predetermined pitch as shown in FIG. 2 is brought into close contact with the photoresist 4 thus coated. The photoresist 4 is exposed to a light 5 for the photoresist sensitization through the photomask 3, and then the development is carried out to remove the photoresist in the exposed area. Further, the metal which is not covered by the photoresist is dissolved and removed by an etching solution. This phase is shown in FIG. 1C. The remaining photoresist 4 is also removed so that the metal layer 2 is exposed in a striped form as shown in FIG. 1D. Onto the glass base plate having thereon such striped metal layer is vapor-deposited a filter material in several layers as illustrated in FIG. 1E. Thereafter, etching is made with respect to the metal layer 2 by using the same etching solution as mentioned above so that the filter material overlying the striped metal layer is removed while the metal layer is dissolved and removed. As the result, the desired stripe filter shown in FIG. 1F is obtained.
In the above mentioned process, three kinds of stripe filters are prepared separately. These stripe filters are aligned at the edge and superimposed one another to produce a stripe filter for extracting three color signals.
The foregoing processes of producing a stripe filter require the alignment, at the edge, of each stripe filter constituting the final stripe filter, which is very difficult to do so with high accuracy.
The applicants have attempted the processes shown in FIGS. 1A-1L and FIGS. 3A-3P for the purpose of producing a stripe filter for extracting different three color signals on a single base plate.
FIGS. 1A-1L show a series of steps for producing a parallel type of stripe filter for extracting two color signals in which two color filter elements, for example those for cyan and yellow are alternatively arranged in parallel to each other on a single base plate. In the steps indicated in FIGS. 1A-1F, a metal capable of being etched, for example aluminum and copper, is vapor-deposited onto a transparent base plate 1, for example made of glass, plastics or the like as shown in FIG. 1A so that a metal layer 2 is formed. A photoresist 4 is then coated on the metal layer as shown in FIG. 1B. On the other hand, a photomask 3 is prepared with high accuracy which has a transparent portion and non-transparent portion, both being alternatively arranged in a striped form at suitable intervals as illustrated in FIG. 2. As shown in FIG. 1B, the photomask 3 is positioned over the photoresist 4 in non-contact state, in contact with the photoresist layer 4 by using an optical printing device. Such photoresist is exposed to a light from a light source for the photoresist sensitization through the photomask 3 and the developing treatment is effected to remove the photoresist 4 in the exposed area. Then, the metal layer 2 which is not covered by the photoresist is etched and dissolved with an etching solution to remove the metal layer as indicated in FIG. 1C. The remaining photoresist 4 in the unexposed area is also removed. This phase is illustrated in FIG. 1D. In the above mentioned manner, there is prepared a plate in which the metal layers 2 are arranged on the transparent base plate 1 in a striped configuration at suitable intervals.
Subsequently, as indicated in FIG. 1E, a dichroic layer 6 (for example cyan) composed of multiple layer film having the pre-determined spectral characteristics is uniformly formed on the transparent base plate 1 and the metal layer 2 by the vapor-depositing method. The metal layer 2 is then removed along with the overlying dichroic layer 6 so that only the dichroic layer 6 on the base plate 1 remains which is arranged in a striped configuration as shown in FIG. 1F.
For the purpose of forming another dichroic layer (for example yellow) having different spectral characteristics, a series of steps described above may be repeated as shown in FIGS. 1G-1L. As shown in FIG. 1G, a metal layer 2 is formed by the vapor-deposition on the transparent base plate 1 having thereon the striped dichroic layer 6, and a photoresist 4 is then coated as indicated in FIG. 1H. Exposure of the photoresist 4 to a light is carried out through the photomask 3 and the development is also effected to remove the photoresist 4 in the exposed area, and thereafter the metal layer 2 in the exposed area is dissolved and removed. This phase is shown in FIG. 1I. Further, the remaining photoresist 4 is also removed so that a plate is obtained which has thereon the dichroic layer 6 and metal layer 2. The latter layer 2 is superimposed on the former layer 6, and the superimposed portion is arranged in a striped configuration as illustrated in FIG. 1J. A dichroic layer 7 (for example yellow) having the pre-determined spectral characteristics is uniformly formed on both the base plate 1 and metal layer 2 by vapor-deposition as illustrated in FIG. 1K. Lastly, the metal layer 2 is removed together with the overlying dichroic layer 7 so that only the dichroic layers 6 and 7 remain which are alternatively arranged on the transparent base plate 1 in a striped configuration as shown in FIG. 1L.
FIGS. 3A-3P show the process of producing a parallel type of stripe filter for extracting three color signals which has been attempted by the applicants. In this process, three color filter elements, that is, cyan, yellow and magenta are successively arranged in parallel to one another. A series of steps in this process is similar to that in producing a parallel type of stripe filter for extracting two kinds of color signals. Therefore, the procedure in the steps of FIGS. 1A-1F is repeated in the steps of FIGS. 3A-3F, FIGS. 3G-3K and FIGS. 3L-3P so that a stripe filter for extracting three color signals is obtained. Such a stripe filter is as shown in FIG. 3P. In addition, reference numeral 8 in FIGS. 3O and 3P denotes a dichroic layer (for example magenta) having the pre-determined spectral characteristics.
However, various disadvantages or defects are pointed out in the processes of producing a stripe filter as described above. In particular, the disadvantages reside in the steps shown in FIGS. 1H and 1I, FIGS. 3H and 3I, and FIGS. 3M and 3N. That is, it is considerably difficult to effect the exposure and development to the photoresist layer 4 so that the line width of such layer may be always constant. Also, when the metal layer is etched, considerable difficulty is found in bring at least one side of the remaining metal layer 2 (in FIGS. 1I, 3I and 3N) in line with one side of the underlying dichroic layer 6. Therefore, it is difficult to finish accuracy the stripe filter to the desired form as shown in FIGS. 1L and 3P. In fact, the finally processed state of the stripe filter actually produced by the process is as illustrated in FIGS. 4 and 5 which are concerned with two-color and three-color stripe filters for extracting two color signals and three color signals, respectively. Various causes for such a state of the stripe filter are considered, for example, an accidental error of the line width of the layers due to the unsuitable position of the photomask 3, change in the viscosity of the photoresist 4 in each step of using it and unevenness in the thickness of the photoresist layer due to the irregularity in the rotation of a spiner used in coating it, change in the exposure amount due to variation in the voltage of the light source and the like, change in the etching amount per the unit time due to change in the composition and temperature of the etching solution, and others. However, it is very difficult to eliminate completely those changing factors. For the purpose of preventing the overlapping of the dichroic layers and eliminating the clearance between them, it is required to employ for higher level of the technique for the production of the parallel type of stripe filter, which is very difficult.